This invention relates to an image processing apparatus, or more precisely, an image processing apparatus using a multiple resolution processing.
The processing section of a radiation image uses a method that adds conversion processing to an original image signal. FIG. 20 illustrates an explanation of a conventional frequency emphasizing-processing. Processed image signals are created by creating unsharp image signal 2 from original image signal 1 generating differential image signal 3 by subtracting said unsharp image signal 2 from original image signal 1, and adding the result of multiplication between coefficient β and said differential image signal 3 to original image signal 1 as a correction signal.
FIG. 21 illustrates an explanation of a conventional dynamic range compression processing. Identical codes are assigned to the items identical in FIG. 20. In this case, differential image signal 3 is generated by creating unsharp image signal 2 from original image signal 1 and subtracting unsharp image signal 2 from original image signal 1. At the same time, compensation image signal 5 is obtained by adding density-compensating conversion 4 to unsharp image signal 2. A processed image signal is obtained by adding differential image signal 3 to said compensation-image signal 5 that was obtained. Recently, a method for obtaining sharper processed image signals has been developed by improving said image processing method.
As one of the techniques, a multiple resolution method is available. Image processing using said multiple resolution method obtains image signals by decomposing an original image signal into image signals of multiple frequency bands, adding specified image processing, and restoring said image signals. Image processing using said multiple resolution method is introduced in (Digital Image Processing: Springer-Verlag 1991). Said document does not describe the processing implemented by applying conversion processing to a unsharp image signal or a differential image signal that is decomposed. A pyramid algorithm is available as one of the algorithms for high speed image processing using said multiple resolution method.
Various methods have been proposed as image processing techniques using said pyramid algorithm. However, filters of mask processing used in said techniques are always in a fixed shape (for instance, Japanese Application Patent Laid-Open Publication No. Hei 10-75395 report). Therefore, frequency characteristics of decomposed image signals are identical and consequently are not suitable for more delicate frequency operations.